The present invention relates to an apparatus for condensing a drafted fiber strand in a condensing zone arranged downstream of the front roller pair of a drafting unit, which condensing zone comprises a stationary sliding surface having a suction slit extending essentially in transport direction of the fiber strand, and a perforated transport belt which transports the fiber strand over the sliding surface, on which transport belt a nipping roller, bordering the exit side of the condensing zone, is disposed.
In the case of an apparatus of this type (German published patent application 197 08 410), the nipping roller is the upper roller of a delivery roller pair, whose bottom roller is looped by the transport belt. The bottom roller in turn is driven by a further drive roller which extends in machine longitudinal direction, so that at the end of the condensing zone three rollers in total are arranged one over the other. This design, which requires a separate drive shaft und gearing from the headstock of the ring spinning machine, is considerably complicated and, in particular, does not permit already existing ring spinning machines to be retrofitted with a condensing zone.
It is an object of the present invention to simplify the complicated drive design for the transport belt, thus creating an opening for existing ring spinning machines not having a condensing zone to be retrofitted with same.
This object has been achieved in accordance with the present invention in that the nipping roller drives the transport belt, the nipping roller in turn being driven by a friction roller, which is pressed, by means of a loading spring, to the nipping roller and also to a roller of the front roller pair.
A friction drive of this type is very simple and makes it possible in particular to maintain to a great extent the peripheral speed of the front roller pair also at the nipping roller. This takes into consideration the fact that the fiber strand has left the drafting unit and should not be additionally drafted in the condensing zone. In addition, a friction drive of this kind is suitable for retrofitting existing ring spinning machines having no condensing zones with same.
Although it is possible that the friction roller, as well as the nipping roller, is disposed at the same time on the driven bottom roller of the front roller pair, it is particularly purposeful when the friction roller is disposed on the upper roller of the front roller pair. It is then possible to arrange the loading spring at the top arm of the drafting unit, which results in a very simple design.
In the case of an apparatus of this type (German published patent application 197 08 410), the nipping roller is the upper roller of a delivery roller pair, whose bottom roller is looped by the transport belt. The bottom roller in turn is driven by a further drive roller which extends in machine longitudinal direction, so that at the end of the condensing zone three rollers in total are arranged one over the other. This design, which requires a separate drive shaft and gearing from the headstock of the ring spinning machine, is considerably complicated and, in particular, does not permit already existing ring spinning machines to be retrofitted with a condensing zone.
The nipping roller can also be designed in a variety of ways. The nipping roller can have a flexible coating, which is provided for the drive effected by the friction roller as well as for the drive of the transport belt. The nipping roller can alternatively be so designed that the flexible coating has two areas, one for the drive effected by the friction roller and one for the drive of the transport belt. The two areas can have in addition different diameters, so that the area with an enlarged diameter driving the transport belt effects a certain tension draft on the fiber strand.
The friction roller, which is advantageously designed as a pressure roller, can have a fitted collar. This makes it possible to design the friction roller simultaneously as a cleaning device for the nipping roller and/or for the upper roller of the front roller pair. The cleaning device can, for example, comprise a lamellar ring fitted onto the collar of the friction roller.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings.